Sustain and Zero Impact are the only 2 bars I'd use if I had to. If it's possible for you to carry your own MRP shakes then I'd do that instead because the MRP formulas are superior to bars IMO.

Sustain bars are good, but I prefer Zero Impact if I'm acually going to use it instead of a meal. 20 grams of protein is a little low... eating 2 bars is too much sugar. Then there is tha whole soy protein debate. Zero Impact's seem to be a happy medium with fewer calories than 2 bars combined.